1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the device, and more particularly to a semiconductor device having an upper wiring layer and a lower wiring layer and a method of forming these wiring layers.
2. Description of the Related Art
A semiconductor device is known which has an upper wiring layer and a lower wiring layer. These wiring layers are connected, forming a VIA contact, by a specific method. This method will be explained with reference to FIGS. 1A to 1C.
First, as is shown in FIG. 1A, a first inter-layer insulation film 2 is deposited on a semiconductor substrate 1 in which various elements have been formed. Next, a first wiring layer 3 (e.g., an Al-alloy layer) is formed on the first inter-layer insulation film 2. A second inter-layer insulation film 4 (e.g., a plasma SiO.sub.2 film) is deposited on the first wiring layer 3. A photoresist 5 is formed on the second inter-layer insulation film 4. The photoresist 5 has an opening formed in a predetermined portion. Then, as is shown in FIG. 1B, anisotropic etching (e.g., reactive ion etching) is performed on the second inter-layer insulation film 4, using the photoresist 5 as mask. As a result, a contact hole 6 is made in the film 4, thus exposing the first wiring layer 3. Further, as is shown in FIG. 1C, the photoresist 5 is removed, and a metal layer (e.g., an Al-alloy layer) is deposited on the surface of the resultant structure, by means of sputtering. The metal layer is patterned, by the known method, into a second wiring layer 7.
The method described above is disadvantageous in two respects. First, as carbon (C) and fluorine (F) are emitted from the photoresist 5 into the plasma during the anisotropic etching, the metals and impurities (C, Cl, F) contained in the fist wiring layer 3 are sputtered onto the periphery of the contact hole 6 made in the insulation film 4, thus forming a metal-containing organic film 8. Secondly, after the hole 6 is made, thus exposing the first wiring layer 3 to the atmosphere, the layer 3 and the chlorine (Cl) on the surface thereof react, thus forming aluminum chloride (AlCl.sub.4), and then aluminum chloride and the water in the atmosphere react, thus forming chlorine ions, as can be understood from the following formulae: EQU Al+4Cl.sup.- .fwdarw.AlCl.sub.4.sup.- +3e (1) EQU 2AlCl.sub.4 +6H.sub.2 O.fwdarw.2Al(OH).sub.3 +6H.sup.+ +8Cl.sup.-( 2)
The more chlorine ions are formed, the more the first wiring layer 3 is corroded. Ultimately, a thick aluminum hydroxide film 9 is formed on the bottom of the contact hole 6, namely on the exposed portion of the first wiring layer 3.
The presence of the metal-containing organic film 8 and the aluminum hydroxide film 9 result in two undesirable phenomena. First, the second wiring layer 7 has overhangs, with the result that some of the wires, but not all, are cut. Second, the electrical connection between the first and second wiring layers 3 and 7 is inevitably impaired.
The conventional semiconductor, whose upper and lower wiring layers are formed by the method explained above, cannot have a sufficiently high integration density. This is because a relatively broad margin must be provided for the alignment between the masks for forming the upper wiring layer 7 and the contact hole 6.